The present invention relates to a new and improved method of, and apparatus for, analyzing particles suspended in a liquid, especially blood cells.
The apparatus of the present invention and useful for the practice of the method aspects thereof is generally of the type comprising two vessels or containers for the suspension and separated by an insulating wall. An elongate channel piercingly extends through such insulating wall. Further, there are connected two supply electrodes each of which is in contact with the liquid in a respective one of the vessels and each such supply electrode being respectively connected to one terminal of an electrical power supply. There is also provided at least one auxiliary electrode which contacts the liquid in the channel, the dimensions of such auxiliary electrode in a direction essentially parallel to the lengthwise direction of the channel being small in relation to the length of the channel. In other words, if the conducting material of the auxiliary electrode would be replaced by an insulating material there would not occur any appreciable change of the current and potential distribution within the channel. There also are provided feeler means, wherein a respective one of such feeler means is operatively associated with a respective one of a pair of electrodes for detecting timewise changes of the potential difference between these electrodes.
Now there is already known to the art apparatus wherein there are detected changes of the potential difference between both supply electrodes and such is evaluated for particle analysis. However, disturbances arise which are predicated upon the turbulence of the liquid and the boundary or fringe effects of the electrical measuring fields. One phenomena which should be mentioned as especially disturbing is that turbulence exists in the vessel which is located at the outlet of the channel in the throughflow direction, this turbulence recycling particles which have already been measured back into the region of the measuring field. Particles which have been recirculated in this manner retrigger a change in the measured potential difference, thus falsifying the measurement result. It has already been proposed to provide a spatial limiting of the suspension in the channel. However, the equipment suitable for exploiting this technique is extremely complicated and correspondingly expensive.
There is also known to the art another type of apparatus wherein, apart from there being provided both supply electrodes, there are additionally employed two auxiliary electrodes between which there are detected changes in the potential difference and evaluated for particle analysis. Through the provision of a suitable arrangement of the auxiliary electrodes the measurement of a particle occurs at that point in time where such is dispositioned at the region of the center of the channel, i.e., at a location where disturbances in the measurement caused by turbulence and boundary phenomena of the measuring field have the least effect. What is however disadvantageous with this state-of-the-art equipment is that the reproducibility of the measurement is dependent upon the constancy of the geometric and electrochemical properties of the auxiliary electrodes. Furthermore, during cleaning of the channel there is required the greatest care in order to prevent any alteration whatsoever of the auxiliary electrodes. The operation of the apparatus is therefore correspondingly complicated, as is also the fabrication of a channel equipped with two identical auxiliary electrodes.